In libraries and on the Internet you can find books, magazines, encyclopedias, lab reports, historical documents, audio and video recordings, and all sorts of other information sources, all of which are useful for different purposes. Deciding which will suit your purpose is an important early step in the research process.
 

Three basic types of resources:

To know where to go for information, it is useful to know how information is produced; here is a very general overview. (note that these are not rigid distinctions; the same resource can overlap categories.)

• Primary - Direct, uninterpreted records of the subject of your research project. A primary source is as close as you can get to the event, person, phenomenon, or other subject of your research. As such, a primary source can be almost anything, depending on the subject and purpose of your research. For example, if you are writing about a novel, the novel is a primary source, and an article critiquing the novel is a secondary source to help you construct your own interpretation of the novel. If you are writing about the critical reception of a novel, that article critiquing the novel is a primary source. Or, a published version (or even a translation) of a diary, if it is a reliable representation of the actual diary, is for many (but not all) purposes sufficient as a primary source. So be creative in thinking of possible relevant primary sources of information on your topic. 
  To make things even more confusing, 'primary source' means something different in science and in humanities (and can go either way in social sciences). In science, an academic journal article presenting the results of a researcher’s original experiment is a primary source. But in the humanities, a journal article is a secondary source which presents the results of the researcher’s analysis and critique of primary sources.
• Secondary - Books, articles, and other writings by scholars and researchers build on primary sources by interpreting and assessing primary information.
• Tertiary - Encyclopedias, indexes, textbooks, and other reference sources which present summaries of or introductions to the current state of research on a topic, or provide a list of primary and secondary sources of more extensive information.

Work backwards. Usually, your research should begin with tertiary sources:

1. Tertiary - Start by finding background information on your topic by consulting reference sources for introductions and summaries, and to find bibliographies or citations of secondary and primary sources.
2. Secondary - Find books, articles, and other sources providing more extensive and thorough analyses of a topic. Check to see what other scholars have to say about your topic.
3. Primary - A primary source on its own is likely only a snippet or snapshot of the full picture; thus it is often difficult to interpret on its own. Reference sources and secondary analyses give you a framework for interpreting primary sources. But the real work of research is examining primary sources to test the interpretations, analyses, and views you find in reference and secondary sources. Now that you have a solid background knowledge of your topic, you are better able to understand, interpret, and analyze the primary source information. Use primary sources to find evidence which challenges these interpretations, or evidence in favor of one scholar's interpretation over that of another; then posit an interpretation of your own, and look for more primary sources for evidence to confirm or refute your thesis. When you present your conclusions, you will have produced another secondary source to aid others in their research.
   
    

Here's a brief list of some of the sources you can find in each of these categories; remember, there are many more:
 

Primary

• Conference proceedings - Scholars and researchers getting together and presenting their latest ideas and findings
• Books - Extensive and detailed discussions of a particular topic or set of topics, written by the scholars and researchers who came up with the ideas or discovered the findings.
• Journal articles - Brief, specific analyses of particular aspects of a topic, written by the scholars and researchers who came up with the ideas or discovered the findings.
• Lab reports - Experiments, observations, etc.
• Historical documents - Official papers, maps, treaties, etc.
• First-person accounts - Diaries, memoirs, letters, interviews, speeches
• Recordings - audio, video, photographic
• Artifacts - manufactured items such as clothing, furniture, tools, buildings
• Newspapers - Some types of articles, e.g. stories on a breaking issue, or journalists reporting the results of their investigations.
• Government publications - Census statistics, economic data, court reports, etc.
• Internet - Web sites that publish the author's findings or research; e.g. your professor's home page listing research results. Note: use caution when using the Internet as a primary source … remember, on the Internet a page citing authoritative findings could have been published by any goofball off the street.
• Manuscript collections - Collected writings, notes, letters, diaries, and other unpublished works.
• Archives - Records (minutes of meetings, purchase invoices, financial statements, etc.) of an organization (e.g. The Nature Conservancy), institution (e.g. Wesleyan University), business, or other group entity (even the Grateful Dead have an archivist on staff).
• Books - collections of historical documents, first-person accounts, archival materials, and other primary sources, compiled and edited by a scholar and published together in a book.
   

Secondary

• Books - Extensive and detailed analyses by scholars providing criticisms, commentaries, and interpretations of primary ideas and findings.
• Journal articles - Brief, specific analyses, criticisms, commentaries, and interpretations of particular aspects of primary ideas and findings.
• Newspapers - Articles which report on earlier findings, or offer commentary or opinions.
• Internet - Web sites that comment on earlier findings or research; see cautionary note above!
   

Tertiary

• Encyclopedias - Articles providing introductory or summary information; coverage can be general (e.g. Encyclopedia Britannica) or subject-specific (e.g. Encyclopedia of Sociology).
• Dictionaries - Definitions or brief summaries of terms, ideas, etc.; coverage can be general (e.g. Webster's, Random House) or subject-specific (e.g. Dictionary of Cell Biology).
• Almanacs - Good for concise factual information, e.g. statistics, lists
• Directories - Lists of people or organizations, with addresses, affiliations, etc.; useful guides to finding primary source material
• Atlases - Maps of population, economic, historical, political, geological, biological, climatological, etc. information.
• Indexes - Lists of sources on a subject or set of subjects; once you have some key terms for your topic, use indexes to find secondary and primary sources.